Three-dimensional shape optimization of fins for application in compact supercritical CO₂ solar receivers

The compact solar receiver is a promising option for S-CO2 solar receivers, designed to operate safely and effi-ciently under high-temperature, high-pressure, and high solar flux conditions. Adding fins with outstanding thermal-hydraulic performance in the mini-channel contributes to maximizing heat transfer performance and minimizing flow resistance for compact solar receivers. However, most of the research on high-performance fins is limited to two-dimensional optimization, ignoring the effect of shape changes in the height direction of the fins. The present study employs a combination of the finite volume method and the adjoint method to optimize single-row cylindrical fin shapes in three-dimensional for compact solar receivers, and the strengthening mechanism of high efficiency and low resistance is further revealed in the view of entropy generation. The results indicate: (1) three-dimensional fins exhibit significant variation in cross-section along the height direction, and each fin is unique; (2) three-dimensional fins exhibit more excellent thermal-hydraulic performance than cy-lindrical fins, showing an increase of 13 % and 20 % in the performance evaluation criterion (PEC) in case 1 (q(w) = 160 kW.m(-2), v(in) = 0.487 m.s(-1)) and in case 2 (q(w) = 584 kW.m(-2), v(in) = 1.778 m.s(-1)), respectively; (3) the entropy generation due to heat transfer is reduced by 4.9% and 3.9%; as well as the entropy generation due to pressure drop is decreased by 8.5 % and 16.5 %, in case 1 and case 2, respectively; (4) robustness results show that three-dimensional fins can maintain higher thermal-hydraulic performance than the initial cylindrical fin even under wide working conditions.